Bipropellant rocket process using nitridable fuel

ABSTRACT

1. The process which comprises burning in a self-sustaining manner and within a rocket combusion chamber having a directional outlet to provide thrust A. A NITRIDABLE FUEL WITH B. AN OXIDIZING NITROGEN SOURCE MATERIAL WHICH SUPPLIES REACTIVE NITROGEN TO SAID FUEL THEREBY EVOLVING REACTION PRODUCTS CONTAINING NITRIDES AND FREE HYDROGEN, SAID NITROGEN SOURCE MATERIAL BEING SELECTED FROM THE GROUP CONSISTING OF GUANIDINE, 1,6-DIAMINO-5-GUANIDINE, 1,4-DIAMINO-DIGUANIDINE TRIAMINOGUANIDINE, 5-AMINO-TETRAZOLE AND HYDROXYLAMINE.

United States Patent Bauman 51 June 13, 1972 BIPROPELLANT ROCKET PROCESS USING NITRIDABLE FUEL [72] Inventor: William C. Bauman, Midland, Mich.

[73] Assignee: The Dow Chemical Company, Midland,

Mich.

[22] Filed: Oct. 14,1959

[21] Appl.No.: 846,509

[52] US. Cl ..60/211, 60/214, 60/215, 149/22, 149/36 [51] Int. Cl ..C06d 5/06, C06d 5/08, C06d 5/10 [58] Field of Search ..52/0.5 L; 60/35.4, 21l-216; 149/22, 36

[ References Cited UNITED STATES PATENTS 10/1951 Malina et al. ..60/35.4

OTHER PUBLICATIONS Penner, Journal of Chemical Education, Jan. 1952 pages 37- 39 Grant, Jr. Journal of Spaces Flight, Vol. 2, N0. 10, Dec. 1950, pages 3- 5 Anderton, Aviation Week, Nov. 12, 1956, pages 51, 53, 55 & 57

Harvey, SAE Journal Vol. 16, Aug. 1957, pages 17- 20 Steindler et al., American Chemical Society, Vol. 75, Jan. 3, 1958 page 756.

Science Newsletter July 10, 1948- page 25 Handbook of Chemistry and Physics- Chemical Rubber Pub. Co. 31st. Edition1949- p. 462.

Vemet-Lozet-lnteravia, Vol. 12, No. 8 August 1957 pp. 799- 801.

Audrieth- The Chemistry of Hydrazine- John Wiley & Sons, Inc., New York 1951) preface p. VIII, P. 101

Primary Examiner-Benjamin R. Padgett Attorney-Griswold & Burdick, William R. Norris and Lloyd 8. Jowanovitz EXEMPLARY CLAIM 6 Claims, No Drawings This invention relates to new rocket propellant systems and new compositions of matter connected therewith. More particularly the present invention concerns highly exothermic chemical reactions of nitridable fuels and oxidizing nitrogen source materials, adaptable for employment in rocket propulsron.

A chemical propellant system is a chemically balanced source of potential energy which is convertible to thrust upon combustion within a rocket motor. The amount of thrust produced is largely dependent upon the chemical and physical properties of a primary reaction between fuel and oxidizer portions of the propellant system. Therefore, it is desirable to provide new primary reaction systems capable of supplying large amounts of energy and relatively low molecular weight products at relatively low combustion temperatures. Improvements in these capabilities provide corresponding increases in thrust and ultimately, rocket performance. Furthermore, low combustion temperatures simplify the design requirements of the rocket combustion chamber and nozzle.

A principal object of the present invention is to provide new and improved high energy rocket propellant systems. A further object is to provide a new class of oxidizing materials for high energy propulsion reactions employing nitridable fuels. Another object of the present invention is to provide a propellant system which upon combustion provides large amounts of energy and relatively low molecular weight reaction products at relatively low temperatures. Other objects will become apparent hereinafter as the invention is more fully described.

The present invention involves a method of developing thrust which comprises reacting, within a combustion chamber of a rocket, a nitridable fuel with an oxidizing nitrogen source material in a manner so as to evolve reaction products containing nitrides and free hydrogen and utilizing the energy thus produced to cause thrust.

Nitridable fuel for the purposes of this specification refers to materials containing at least one elemental component capable of forming a nitride in a self-sustained high energy reaction with a nitrogen providing oxidant. Preferably, nitridable fuels contain such low molecular weight elements as beryllium, boron, aluminum and titanium. Specific nitridable fuels operable in the present invention in addition to the above mentioned elements include, for example, diborane, pentaborane, decaborane, beryllium borohydr-ide, aluminum borohydride, aluminum hydride, beryllium aluminum hydride and the like compounds.

Oxidizing nitrogen source materials for the purposes of this specification refers to compositions capable of supplying reactive nitrogen, under reaction conditions required for selfsustained combustion of a nitridable fuel. In addition to the necessary nitrogen, it is desirable that such compositions contain a substantial molar proportion of hydrogen in combined form. They may also, however, contain lesser amounts of other elements such as oxygen and carbon.

Oxidizing nitrogen source materials operable in the present invention include, for example, hydrides of nitrogen such as ammonia, hydrazine, triazine and S-amino tetrazole. Others are guanidine, triamino guanidine, 1,4-diaminobiquanidine and the like compounds.

Frequently, it is desirable to improve the storage stability of certain oxidizing nitrogen source materials such as the guanidines by employing them in the form of an acid salt. Of the acids, nitric, nitrous, chloric, perchloric and hydrofluoric are preferred since the acid radicals are capable of supplying part of the required oxidizer.

It should be understood that the present invention can be employed conjunctively with conventional propellant oxidizers. Other oxidants such as oxygen, fluorine and compounds containing these materials in combined form, may have preferential reactivity with the nitridable fuel as comnitrides can be formed in the presence of oxides or fluorides when less than the full stoichiometric requirement of such other oxidants is employed in conjunction with an oxidizing nitrogen source material.

A unique oxidant having potential within the scope of the present invention is hydroxylamine Nrnorr It is capable of supplying both oxygen and nitrogen in a reactive form. in a combined reaction, one mole of hydroxylamine provides, at full stoichiometry, two equivalents based on the oxygen and three equivalents based on the nitrogen to make a total of five possible equivalents. Since oxygen as compared with nitrogen is preferentially reactive with the nitridable fuels of the present invention, the presence of more than two equivalents of fuel for each mole of hydroxylamine reacted is necessary before nitrides are formed. When less than two equivalents of fuel are employed for each mole of hydroxylamine, only the oxides of the fuel are formed. As a source of oxygen, hydroxylamine can also be used effectively as the oxidant for fuels containing magnesium and lithium as well as the nitridable fuels. Hydroxylamine must be stored either at a temperature of about zero degrees centigrade or as a salt of an acid such as hydrofluoric or nitric in order to maintain stability.

In carrying out the present invention, the foregoing nitridable fuels and oxidizing nitrogen source materials can be employed either in liquid propellant systems or in solid propellant systems. The actual mode of use is dependent upon the inherent physical character of the foregoing nitridable fuels and oxidizing nitrogen source materials.

The reactants of liquid bipropellant systems are usually separately stored and mixed either just before injection into the combustion zone or within the combustion zone itself, and are injected into the combustion zone by means of high pressure pumps above a minimum rate sufficient to maintain a self-sustained reaction.

In solid propellant systems the nitridable fuel and the oxidizing nitrogen source material may exist within a propellant mixture as individual compounds or in some instances, as a single compound. In the former instance, they are known as composite solid propellants and in the latter, they are known as homogenous or solid monopropellants. Solid propellants are burned in situ and thus require a minimum of rocket hardware" for their utilization.

Generally, whether the present invention is employed as a liquid bipropellant, liquid monopropellant, solid composite propellant or a solid homogenous propellant, at least stoichiometric quantities of the oxidizing nitrogen source materials are reacted with a nitridable fuel. In monopropellant systems, at least part of the oxidizing material and fuel can exist as a single compound but in the instances of solid composite propellant systems and liquid bipropellant systems, the reaction ingredients are usually separately maintained until or slightly before the instant of reaction.

Reaction pressures can vary from one atmosphere to the upper design limit for the rocket motor. As the pressure at which the propulsion reaction is carried out is increased, the specific impulse obtainable from that system is also increased. For example, in raising the reaction pressure from 500 to 1,000 pounds per square inch absolute, the specific impulse of most systems within the scope of the present invention is increased by a factor of approximately 7 percent. It is desirable to carry out propulsion reactions of the present invention at pressures of about 1,000 pounds per square inch absolute.

A propulsion reaction between nitridable fuels and oxidizing nitrogen source materials in accordance with the present invention is a non-hypergolic reaction, but a self-sustained reaction can be initiated by means of an auxiliary ignition device. An ignition device capable of sustaining a temperature of about l,700 Kelvin for a period of about 1 to 5 seconds is generally sufiicient for the initiation of a self-sustaining reaction in accordance with the present invention. However, optimum ignition conditions will vary with particular mixtures and higher temperatures and longer times may be necessary. See Warren, Rocket Propellants, Reinhold Pub. Corp., 1958),

pared to oxidizing nitrogen source materials; however, the pp. 108-25.

The flame temperature of the reaction is dependent upon inherent properties of the particular ingredients employed and the products formed. Usually, an effective reaction flame temperature cannot be obtained above disproportionation or phase change temperatures of the metal nitride reaction products. Thus, in order to optimize thrust, it may be desirable to maintain the ambient combustion chamber temperature at temperatures lower than the flame temperature of the reaction by the addition of an enhancing material to the combustion zone.

To optimize the thrust output of a particular reaction system of the present invention, it may be desirable to employ an enhancing material. Enhancing material does not enter into the primary propulsion reaction. It is added to the combustion zone of the primary propulsion reaction to utilize for the production of thrust transitional heat of transformations, i.e., phase changes or disproportionation,in the reaction products, and to improve thrust by lowering the average molecular weight of the exhausting products. A vaporizable substance, which requires relatively little heat energy to be raised to a temperature near the flame temperature of the reaction and which has either a low molecular weight itself or a capacity to dissociate into low molecular weight gaseous products upon the application of heat can be employed in the presence of the primary propulsion reaction as an enhancing material. A most effective enhancing material has a positive heat of formation so that upon dissociation it supplies part of the heat required to raise its products to the desired chamber temperature. Enhancing materials contemplated for use in conjunction with the present invention include ammonia, hydrazine, triazine, guanidine and the like.

If employed, such enhancing materials are used in an amount sufficient to maintain a combustion chamber temperature below that at which high temperature transformations such as phase changes or disproportionation occur in reaction products and at a temperature correlative with an optimum improvement in thrust resulting from lowering the average molecular weight of the reaction products.

For a more complete description of the manner of use of enhancing materials, see my copending application Ser. No. 846,510, filed Oct. 14, 1959.

In addition to basic reactants and the optional enhancing materials, other materials frequently incorporated in the propellant systems include such specific agents as ignition promoters, freezing point depressants, corrosion inhibitors, binders, catalysts and the like.

In the practice of the present invention it is often possible to achieve an average molecular weight in the exhausting products of 20 or less with such products being gaseous or substantially gaseous in nature. Generally, any solid products produced are highly amorphous and extremely fine particles capable of achieving, within practical limits, kinetic equilibrium with the gaseous products in the thrust producing exhaust. Also, these extremely fine particles are in the form most desirable for achieving complete transfer of transitional heats to gases derived from enhancing materials.

A direct advantage of employing nitrogen as an oxidizer is its lower equivalent weight of 4.67 as compared to the equivalent weights of prior propellant oxidants such as oxygen having an equivalent weight of 8 and fluorine having an equivalent weight of 19. Also great benefit is derived in the practice of the present invention from the high molar concentration of hydrogen in oxidizing nitrogen source materials. This hydrogen evolves from the combustion reaction as free hydrogen and as the concentration of hydrogen is increased in the combustion products, their average molecular weight asymptotically approaches a lower limit of 2 which is ideal for the production of thrust.

The following is exemplary of the primary reaction systems of the present invention:

8 1-1 N l'hm 2BN 5H Heat In computing the specific impulse for the above system and the others tabulated below the reaction products are assumed to be ideal gases and their expansion through a rocket nozzle is assumed to be adiabatic. Although the effect of molecular size is assumed to be negligible, corrections are incorporated for solids in the reaction products. The equation employed to compute the specific impulse is as follows:

Isl Specific Impulse) wherein T chamber temperature in degrees Kelvin, M, the average gram molecular weight of the gases in the exhaust product, M, the average gram molecular weight of the solids in the exhaust, N, the number of moles of solid per mole of gas formed, C, the heat capacity of the solids in calories per gram mole per degree Kelvin, C, the heat capacity of the gaseous products at constant pressure in calories per gram mole per degree Kelvin, (J,- the heat capacity of the gaseous products at constant volume in calories per gram mole per degree Kelvin, P, the exhaust pressure (assumed to be 14.7 psia), P the chamber pressure (assumed to be 500 or 1,000 psia as specified), R the universal gas constant, and 'y Cp/Cv.

By substituting the appropriate values of the foregoing variables into the above equation, the specific impulse of the diborane-hydrazine propulsion system was found to be 348 pound seconds/pound. Exemplary specific impulses of other systems of nitridable fuels and oxidizing nitrogen source materials are set forth below.

Approx. specific impulse Oxidizing nitrogen source material (P,,=500) (P,,=1,000) Nitridable fuel (moles) (moles) p.s.i.a. p.s.i.a.

B (sol.) 1 NQH; (liq.) 284 pg BiH (11q.), plus V N H; (1iq.) 314 336 34 BiH (1111.), plus 1 NH; (liq 281 299 M0 BioHu (501.), 131118 1 NHa (liq 280 1 BwHu (sol.), plus. CNrHs 296 1 BmHzoNr (501.) pl NH3 (11 279 1 B HmNr' (sol.), plus 1 CNaHs (sol.) 291 1 Be (EH (sol.), plus--. 4 NzH4 (liq.) 292 312 3 BeH (sol.), plus 1 NQH4 (liq.) 308 330 1 Be (EH (sol.), plus... 1 NHzOH (sol.)

plus 1 NH; (liq.)-. 338 362 1 Ba (BHm ($01.), plus... 1 NHgOH (sol.)

plus N H (1iq.) 330 354 1 Be (EH (sol.), plus-.. NHQOH (sol.) 326 350 A B10H10N4=dlhydf81ll1l3 adduct of decaborane. b CNoHa=tri amingguanidina Another typical propulsion reaction in accordance with the present invention involves reacting the dihydrazine adduct of decaborane with sufficient additional hydrazine to provide a stoichiometrically balanced reaction system. The dihydrazine adduct of decaborane is prepared from B I-I '2CH,CN (BAND), [see Schaeffer, J.A.C.S., Vol. 79, pp. 1006-7, 1957)]and hydrazine. A stoichiometric amount of hydrazine is refluxed with band in the presence of benzene. The benzene is then decanted from the reaction mixture and a precipitating agent such as water or ethanol is added to the product. The desired product is then separated by filtration.

The mixture of one mole equivalent of the adduct in 3 mole equivalents of hydrazine is a slurry having a specific impulse of approximately 304 pound seconds/pound. However, when about twice the stoichiometric quantity of hydrazine is employed, the mixture becomes a liquid solution. Liquids form when from 5.75 to 9 moles of hydrazine per mole of decaborane are employed. As a liquid, such a composition is an effective monopropellant having a specific impulse of about 296 pound seconds/pound. In spite of the excess hydrazine employed, the specific impulse is only about 3 percent less than the specific impulse obtainable from a stoichiometric reaction.

The following Examples illustrate the concept of the present invention and should not be construed as limitations thereof.

A vertical reaction vessel consisting of a 2% inch by 48 inch Pyrex tube was fitted with a 16 inch tungsten wire filament, centrally positioned along the longitudinal axis of the tube. The filament was connected by means of wire leads to an outside variable electric power source. At its top the tube was fitted with a vacuum measuring device and connected to separate regulated sources of supply for each reaction ingredient. Near its bottom the tube was connected to a vacuum pump and an effluent product train consisting of a series arrangement of a sulfuric acid trap for unreacted products and a wet gas measuring meter.

The reaction system was evacuated, flushed with helium, and allowed to remain at 1 atmosphere of helium pressure. The tungsten filament was electrically heated to a temperature of about 1,650" as measured with a visual pyrometer. Each of the reactants was then metered into the reaction vessel for a period of time of about 1 hour. Ammonia was supplied at a rate of about 120 cc. per minute and diborane was supplied at a rate of about 62 cc. per minute, while helium, a non-reacting diluent, was supplied at a rate of about 140 cc. per minute. All volume measurements are corrected to constant temperatures and pressures.

The effluent gas as measured by the wet gas meter consisted of only helium, nitrogen and hydrogen since all other gases and solid products were removed in the acid trap. After the reaction had begun, the effluent gas flow rate stabilized at about 310 cubic centimeters per minute. The flow of helium, ammonia and diborane was ultimately stopped and the wire allowed to cool. Samples were collected from the finely particulate powder coatings on the tungsten wire and the adjacent tube walls. X-ray diffraction analyses of the samples showed the presence of boron nitride.

EXAMPLE ll Samples of B H, -2(N H (the dihydrazine adduct of decaborane) were dissolved in an amount of hydrazine which was about twice the stoichiometric requirement for complete conversion of the boron to boron nitride. A sample of 7.7 grams of a mixture containing hydrazine and B, H, '2(N H in a molar ratio of 6.7 to 1, respectively, was placed in a 980 cubic centimeter force bomb. The bomb was then twice flushed out with argon at 150 pounds per square inch gauge. Ignition was accomplished by passing about 12 amperes of direct current through a, No. 19 gauge nichrome wire, which was positioned in the proximate vicinity of the test mixture within the bomb, for a period of about 2 minutes.

Three other test mixtures were prepared at mole ratios of hydrazine to B, H '2(N l-l of 7.2, 7.9 and 8.05, respectively, and reacted in a manner similar to that of the foregoing run.

The average of these relative force bomb measurements corresponded to a specific impulse at 1,000 pounds per square inch absolute of approximately 252 pound seconds/pound. The reaction products included a solid product which was a gray fiufiy solid shown by x-ray diffraction analysis to containboron nitride and an unidentified compound containing in addition to boron and nitrogen, about 4.5 percent hydrogen.

In a manner similar to that of the foregoing examples, other propulsion reactions can be carried out wherein a nitridable fuel selected from the group consisting of beryllium, boron, aluminum, titanium, pentaborane, decaborane, aluminum hydride, titanium hydride, beryllium borohydride and aluminum borohydride is substituted for the diborane in the foregoing examples achieving thereby comparable results.

Similarly, in the manner of the foregoing examples, other oxidizing nitrogen source materials selected from a group consisting of triazine, guanidine, l,4-diamino-diguanidine, triamino quanidine and 5-amino-tetrazole can be substituted for the hydrazine in the foregoing example with the achievement therebyofcom arable results.

In a manner simiar to that of the foregoing examples,

hydroxylamine can be substituted for hydrazine as the oxidizing nitrogen source material when more than two equivalents of the nitridable fuel are employed, thereby achieving comparable results. Efficacious results are also obtained when hydroxylamine is employed as an oxidant for a fuel selected from the group consisting of lithium, magnesium and nitridable fuels.

Various modifications can be made in the present invention without departing from the spirit and scope thereof and it should be understood that the invention is limited only as defined in the claims.

I claim:

1. The process which comprises burning in a self-sustaining manner and within a rocket combusion chamber having a directional outlet to provide thrust a. a nitridable fuel with b. an oxidizing nitrogen source material which supplies reactive nitrogen to said fuel thereby evolving reaction products containing nitrides and free hydrogen, said nitrogen source material being selected from the group consisting of guanidine, 1,6-diamino-5-guanidine, l,4- diamino-diguanidine triaminoguanidine, S-aminotetrazole and hydroxylamine.

2. A method as in claim 1 wherein the oxidizing nitrogen source material is stabilized in the form of a salt of an acid.

3. A method as in claim 1 wherein the oxidizing nitrogen source material is guanidine or an aminated derivative thereof.

4. A method as in claim 1 wherein the oxidizing nitrogen source material is S-amino-tetrazole.

5. A method as in claim 1 wherein the oxidizing nitrogen source material is hydroxylamine.

6. A method as in claim 1 wherein the nitridable fuel is selected from the group consisting lithium, magnesium of beryllium, boron, aluminum, titanium, diborane, pentaborane, decaborane, aluminum hydride, titanium hydride, beryllium borohydride and aluminum borohydride. 

1. THE PROCESS WHICH COMPRISES BURNING IN A SELF-SUSTAINING MANNER AND WITHIN A ROCKET COMBUSTION CHAMBER HAVING A DIRECTIONAL OUTLET TO PROVIDE THRUST A. A NITRIDABLE FUEL WITH B. AN OXIDIZING NITROGEN SOURCE MATERIAL WHICH SUPPLIES REACTIVE NITROGEN TO SAID FUEL THEREBY EVOLVING REACTION PRODUCTS CONTAINING NITRIDES AND FREE HYDROGEN, SAID NITROGEN SOURCE MATERIAL BEING SELECTED FROM THE GROUP CONSISTING OF GUANIDINE, 1,6-DIAMINO-5-GUANIDINE, 1,4DIAMINO-DIGUANIDINE TRIAMIOGUANIDINE,5-AMINOTETRAZOLE AND HYDROXYLAMINE.
 2. A method as in claim 1 wherein the oxidizing nitrogen source material is stabilized in the form of a salt of an acid.
 3. A method as in claim 1 wherein the oxidizing nitrogen source material is guanidine or an aminated derivative thereof.
 4. A method as in claim 1 wherein the oxidizing nitrogen source material is 5-amino-tetrazole.
 5. A method as in claim 1 wherein the oxidizing nitrogen source material is hydroxylamine.
 6. A method as in claim 1 wherein the nitridable fuel is selected from the group consisting lithium, magnesium of beryllium, boron, aluminum, titanium, diborane, pentaborane, decaborane, aluminum hydride, titanium hydride, beryllium borohydride and aluminum borohydride. 